Where does “Ó Cathasaigh” come from?

Ó Cathasaigh (Irish) comes from Irish Ó, from Irish ua, from Old Irish áue, from Primitive Irish ᚐᚃᚔ, from Proto-Celtic awyos, from Proto-Indo-European h₂ewh₂yos — grandfather.

Ancestry of “Ó Cathasaigh”, step by step

StepLanguageWordMeaning
1IrishÓAlternative form of ó used in surnames
2IrishuaArchaic form of ó
3Old Irisháuegrandson
4Primitive Irishᚐᚃᚔdescendant
5Proto-Celticawyos—
6Proto-Indo-Europeanh₂ewh₂yosgrandfather
Every word from Proto-Indo-European h₂ewh₂yos →Every word from Proto-Celtic awyos →Every word from Primitive Irish ᚐᚃᚔ →